Arnold & Maria'sSon Hospitalized-- Surfing Accident

7/22/2011 10:30 AM PDT

Arnold & Maria's Son Hospitalized -- Surfing Accident

Arnold Schwarzeneggerand Maria Shriver's 13-year-old son Christopher is hospitalized after a serious surfing accident last weekend ... so serious he has been in ICU for days ...TMZ has learned.

Christopher suffered multiple broken bones and a collapsed lung as a result of the accident in Malibu. We're told Christopher's condition has now been upgraded and he will be OK .

We're told Maria has constantly been at Chris' side. And Arnold has been a regular visitor as well. We're told in spite of the divorce, the entire family has come together as a unit in dealing with Christopher's accident.

Maria has had an incredibly tough year ... and an extremely rough week.

UPDATE: Arnold just stopped by the hospital to check up on Christopher ... with his daughter Christina in tow. Maria arrived on her own soon after.